According to a new study, cancer patients who are prescribed opioid drugs to reduce pain are more likely to suffer from cognitive deficits than other patients. In the new study, patients on opioids, particularly on high doses of them, were more likely to report memory and attention problems, disorientation, and confusion.

Over 1,900 cancer patients at various hospitals around Europe were tested for cognitive dysfunction. The patients had been prescribed by their doctors various opioid medications, like morphine and oxycodone, for pain management.

Almost 33% of the patients showed signs of possible or definite cognitive dysfunction.

The standard cognitive tests given by the researchers in the current study (known as the mini-mental state examination, or MMSE) measured how well the patients could recall memorized words, as well as other skills like attention, orientation, and language. The best possible score for the test is 30; anything below 23 is considered to imply definite cognitive dysfunction, and scores of 24-27 point to possible dysfunction.

Almost 33% of the patients showed signs of possible or definite cognitive dysfunction. The team found that patients who were on at least 400 mg of opioid medication per day had a 75% greater likelihood of suffering from cognitive dysfunction, compared to patients on 80 mg/day or less. Patients with lung cancer were especially likely to show signs of cognitive dysfunction.

The mechanism by which the medications might lead to cognitive dysfunction is unclear. But it’s important to realize that the study does not suggest a definite causal effect between opioids and cognitive dysfunction — just an association. Other studies have found that other classes of medication, like benzodiazepines, are also associated with higher risk for cognitive problems in patients. It is still unclear, as the researchers point out, whether the cognitive deficits seen in the study are reversible or irreversible after treatment is over with. More research is clearly needed to explore the association further, since pain management is a common and often crucial part of cancer treatment. Please speak with your doctor if you have any questions about medications prescribed to yourself or a loved one.

The research was carried out by a team at Copenhagen University Hospital, and published in the February 28, 2011 online issue of the Journal of Clinical Oncology.